1. Field of the Invention
The invention relates to a system and a method for using location information to determine traffic conditions and/or route conditions or limitations such as, for example, limitations or rules pertaining to a location or a route.
2. Discussion of the Related Art
Methods for determining the position of vehicles, airplanes, and ships include, for example, time difference of arrival (TDOA), angle of arrival (AOA), ray tracing/pattern recognition, global positioning system (GPS), and hybrid methods using network connections. Among the available methods, GPS includes a plurality of satellites orbiting the earth and sending out, at precisely synchronized times, a code sequence that identifies the satellite. Specifically, the code sequence transmitted by each satellite is a precisely timed binary pulse train. In addition to the code sequence, these satellites send out positioning information that can be used to calculate vehicle positions. A GPS receiver retrieves the positioning information from the GPS satellites and triangulates the information to obtain the position of the receiver. A more detailed discussion of a GPS receiver is found in U.S. Pat. No. 5,990,827 to Rodric C. Fan, et al. entitled “Structure of a Position Processing Apparatus,” which is herein incorporated in its entirety.
In using GPS to locate vehicles, each vehicle is equipped with a GPS receiver and a wireless transmitter. Using the GPS receiver and the transmitter, the vehicle determines its position and transmits the position to a ground station. The ground station of a conventional vehicle locating system normally includes a map database search system and some type of storage medium that stores digital maps and travel-related information. Thus, upon receiving the vehicle positions from the mobile units, the ground station combines the stored data with the received information and displays the present vehicle positions on a digital map.
In some cases, a data network, such as the Internet, is involved in locating vehicles. When a data network is involved, the vehicle determines its position and transmits the position information to a network server. This data transmission from a vehicle to the network server is accomplished wirelessly by, for example, cellular digital packet data network (CDPD) that connects to a data network (e.g., the Internet), which in turn provides access to the network server. In some cases, the mobile units may transmit raw data to the network server so that the network server can make the position determination. In a system that involves a network server, the data storage medium may be accessed by the network server instead of the ground station. The data storage medium contains travel-related information such as maps, traffic conditions, positions of service stations, and destinations of interest. Thus, the data processing unit organizes the measured position and generates an area map. The area map indicates by a position marker the position of each mobile unit.
As mentioned above, vehicles can connect to data networks (e.g., the Internet) wirelessly through communication networks, for example a CDPD network. CDPD networks consist of Mobile Data Intermediate Systems (MDISs), Mobile Data Base Stations (MDBSs), and Mobile End Stations (MESs). An MDBS offering CDPD services helps a roaming MES register with the MDIS with which the particular MDBS is associated by acting as a conduit for the registration message. An MDIS that handles the registration is referred to as the serving MDIS. Upon receiving the registration message from the MDBS, the serving MDIS informs the home MDIS of the MES of the latter's presence in its coverage area. When a host needs to send data to an MES, it does not have to be aware of the mobility aspect of the MES; it simply transmits data using the MES's IP address as the destination address. The encapsulated data packets for the MES are forwarded to the serving MDIS of the MES. At the serving MDIS, packets are decapsulated to reveal the MES's address. The serving MDIS sends the original data packets to the right channel where the MES is currently located. The MES receives the data packets. If the MES needs to reply, it directly sends data packets using the remote host's IP address as the destination address. CDPD systems are further described in K. Budka et al., “Cellular Digital Packet Data Networks.” Bell Labs Technical Journal, Vol. 2, No. 3 (Summer 1997); “Cellular Digital Packet Data Systems Specification: Release 1.1,” CDPD Forum, Inc., Chicago (1995); and M. S. Taylor et al., “Internet Mobility: The CDPD Approach,” Prentice Hall PTR, Upper Saddle River, N.J. (1996).
With automobiles being the primary mode of transportation for many individuals and organizations, access to real-time traffic information is desired. Traffic information is a combination of several different types of data, such as for example, the number of vehicles on certain road segments, the average speed of the vehicles, and occurrence of accidents. Currently, traffic information is gathered through means such as television cameras disposed at primary points of a road, or through cameramen and reporters in helicopters. As a result, traffic information is available only for certain roads and is not frequently updated. A way of providing travelers with traffic-related information that would minimize travel time or provide certain information regarding a current or intended route is desirable.